Various types of clamps and brackets are known in the art for the purpose of attaching cross-arms, transformers and other equipment to wooden poles. Blackstone U.S. Pat. No. 2,708,087 discloses six centerpoise transformer racks that are placed in sets of three about a pole and held one to the other by curved T-bolts, the T-heads thereof engaging shaped slots in the racks.
Hamilton U.S. Pat. No. 1,898,725 shows a cross-arm clamp comprising two generally L-shaped brackets having inclined extensions at one end through which an attaching bolt is inserted. The other ends of the brackets adjustably attach to each other by means of an upstanding ear or head on one of the brackets that engages a hole in the other. A wedge lock is also used.
A guy wire attachment is shown in Petersen U.S. Pat. No. 2,703,216 which includes a pair of cleats tied around the pole by a plurality of cables and an adjustable clamp. Ward U.S. Pat. No. 2,761,643 uses as a cluster mount a series of straps or curved plates tied with bolts around the pole with a pair of racks which project radially outward and provide at their ends a further adjustable plate for attachment to transformers of different sizes and weights.
Anderson U.S. Pat. No. 2,879,964 provides a shaped plate having a U-shaped cross section with a central elongated indentation to encompass a part of the circumference of the pole to be held by lag bolts screwed into the pole. A pair of narrower deeper U-shaped plates bolt over the shaped plate to provide a mounting for a third transformer.
Salmon et al. U.S. Pat. No. 3,374,978 provides three elongated bearing plates of generally U-shaped cross section which fit in circumferentially spaced positions against the sides of the pole. The radially directed side flanges of the bearing plates each have a pair of elongated vertical slots. The outer portions of the flanges on each plate are shaped to receive and be encompassed by a pair of diverging bolt-on U-shaped brackets. Two pairs of connecting links and a pair of attaching brackets are provided to engage the opposing spaced slots of adjacent pairs of bearing plates and thereby encompass the pole's circumference. Each end of the connecting links and the remaining ends of the attaching brackets have a series of inwardly directed parallel spaced hooks or projections that engage the inner edges of the respective slots in the flanges of the bearing plates to provide an adjustable girth for different diameter poles. Lock bolts are provided to hold and urge the connecting links toward the pole during the initial assembly steps and lock them against outward movement. The attaching brackets of Salmon et al are reversible on each bearing plate to accommodate smaller transformers.